Did you know that there are differences between pipe and tube? The main differences are in the terminology used and is commonly misunderstood and becomes confusing when trying to choose the proper material for your project Both pipe and tube have two important measurements: The Outside Diameter (O.D.) and the Wall Thickness. In the pipe and tube bending industry the most important difference between the two is the terminology used when calling out the proper “name” when referring to the size of material, and in the proper “name” of their wall thicknesses.. When you measure pipe by its O.D. (Outside Diameter), the true measurement is not what the pipe’s proper “name” will be called out as. Contrary to a tube’s proper “name”, its actual O.D., a pipe’s proper “name” is called out by what we call the Nominal Pipe Size which is NOT the pipe’s actual O.D. measurement. For example what is traditionally called “1-1/2 in. pipe” actually has an O.D. measurement of 1.9 inches, NOT the 1.5 inches that you would think it is. Pipe comes in a variety of Schedules (Sch), which refers to the wall thickness of the pipe. Popular Schedules of pipe are Sch 5, 10, 40, and 80. Unlike tube gages that remain consistent among the O.D.s, the measurement of a pipe’s Schedule varies among the pipe sizes, but the O.D. will remain the same regardless of the Schedule of the pipe. A pipe’s O.D. will remain the same among the different pipe Schedules. It is the Schedule that will vary among the Nominal Pipe sizes. So this means a “1-1/2 in. pipe” will have different I.D.s depending on the Schedule of that particular pipe size, therefore, the Nominal Pipe Size will NOT equal the pipe I.D. (See example below) The pipe I.D. can be calculated by taking the pipe outside diameter and subtracting 2x the wall thickness from it.